A wide range of service robots have been developed so far along with an increase in interest in and demand for service robots, but are not activated as compared to existing industrial robots. It is widely believed that the main cause of such phenomenon is that the price of the existing service robots developed is significantly high as compared to the performance thereof. In particular, because the price of a robot arm capable of performing a work such as gripping and moving an object is greatly high, the current service robot market is limited to just cleaning robots. Thus, the optimization of the price of the robot arms through the development of low-cost robot arms is essential to activate the service robot industry.
A variety of mechanical and electronic components are used in the actual design and production of the robot arms. The cost spent on purchasing a speed reducer and a motor constituting a joint of a robot, and a motor controller reaches up to 90% of the production costs. Recently, most robot arms employ low-cost but high-performance motors and speed reducers in order to ensure work performance (payload, driving speed, work space, etc.). This contributes to an increase in the entire cost of the robot arms, which makes it difficult to form a robot arm market.
A gravity compensation mechanism as a representative method developed for the optimization of the price of the robot arms refers to a mechanism that counterbalances gravitational torques generated by the robot mass at robot joints to minimize torques which are necessary to perform the work.
Korean Patent Laid-Open Publication No. 10-1994-0006726 discloses a gravity compensation mechanism for a robot. However, such a gravity compensation mechanism entails a problem in that since it should be mounted at a shoulder part, a considerable mounting space is needed, or smooth compensation of high resolution is not easy due to a considerable range of a compensation force for a rotation angle of a link center. Since the gravity compensation mechanisms that have been developed so far are designed so as to be mainly applied to industrial robots, their size and counterbalancing method are difficult to apply to the service robot arms. In addition, the existing developed gravity compensation mechanism for a service robot arm is not easy difficult to apply to a multi-degree-of-freedom (DOF) mechanism and as well as is difficult to apply to an actual robot arm due to complexity of the mechanism. Therefore, there is a need for the development of a multi-degree-of-freedom (DOF) counterbalance mechanism which can be applied to an actual robot arm in order to develop a low-cost robot arm.